Laminated electromagnetic core construction



Dec. 7, 1965 A. E. FEINBERG ETAL 3,222,626

LAMINATED ELECTROMAGNETIC CORE CONSTRUCTION Filed June 29, 1961 7 5 I ezce CEemZ United States Patent 3,222,626 LAMINATED ELECTROMAGNETIC CORE CONSTRUCTION Albert E. Feinberg and Eugene Czernobil, Chicago, Ill.,

assignors to Advance Transformer Co., Chicago, Ill., a

corporation of Illinois Filed June 29, 1961, Ser. No. 120,656 6 Claims. (Cl. 336-210) This invention relates generally to electromagnetic core constructions, and more particularly is concerned with laminated electromagnetic core constructions assembled with the use of cementitious bonding media.

The electromagnetic devices with which this invention is concerned comprise iron cores formed of laminated electrical sheet steel, and having coils or windings mounted thereon. The invention herein evolved as a result of investigations directed towards the production of highly economical ballasts for use in gaseous discharge device circuits, but it is believed that the invention has much broader application.

Many transformers used in ballasts for gaseous discharge device circuits are presently formed as shell structures, usually of elongate configuration, having an outer rectangular frame-like portion and a central elongate winding leg extending between the bridged ends of the outer frame-like portion. Windings are mounted on the central winding leg disposed in windows formed between the said central winding leg and the side legs of the outer frame-like portion. Such an assemblage is provided with terminal boards or strips providing electrical terminals for the windings and facilitating the connection of the electromagnetic device into a circuit. The core is rigidly held together, and the entire device is usually encapsu lated by a suitable potting compound in a metallic canister along with other elements, such as condensers, resistors, etc., with terminal leads protruding from the canister.

The shell type core is quite popular because in recent years it has been possible to manufacture the same from so-called scrapless laminations as taught, for example, in US. Patent No. 2,892,249 and others. Such core is formed of stacks of T and L or T and F laminations instead of being formed of laminations of the type shown, for example, in Feinberg Patent No. 2,558,293. In this patent the shell type core is formed of an integral onepiece outer frame portion having the central winding leg frictionally engaged inside the bridging ends. This is a so-called forced core.

The problem which has arisen with respect to so-called scrapless variety of electromagnetic cores is that the core is made up of three elongate metallic members, namely the center winding leg which is usually in the form of a T and the outer portions which are usually in the form of Us or Fs. Not only is it required that the stacks of laminations themselves be maintained in assembly condition, but likewise it is necessary that the three core parts be held together in some manner by suitable means.

It has heretofore been customary to use a metallic clamp with spring fingers in the form of a cap secured over each end of the core after the windings have been associated thereon, and by such structure mechanically holding the core in assembly.

The use of metallic clamps has been a source of certain disadvantages, especially the production of noise. It is difficult to manufacture the clamps with such structure as rigidly to hold every one of the laminations immovably. Variations in dimensions of the laminations result in vibration giving rise to buzzing and humming because of metal contact. There may be many sources for such noise. The stacks of the respective parts may not be the same height; the dimensions of the individual laminations may not be identical; there may be variations in the configuration and resilience of the spring fingers of the clamps; the engagement of the clamps upon the laminations and the laminations upon one another may not be perfect.

Clamps are also quite expensive because they have to be made with highly specialized steels, heat treated for forming spring fingers and using complicated tools and dies. Furthermore, they add to the weight of the ballast. In certain cases, they can cause adverse effects on the magnetic characteristics of a transformer or inductor by providing parasitic paths or undesirable leakage of flux.

The invention herein overcomes all of the objections and disadvantages above enumerated and many others, which will become apparent, by providing a core for an electromagnetic device constructed with the use of a curable cementitious or adhesive material for bonding the stacks of laminations together, and as well for bonding the respective laminations of each stack one to the other. This comprises an important object of the invention.

The invention has as another object thereof the utilization of a poly-merizable resinous material during the formation of a core assembly, said resins curing or setting cycle is characterized by the presence of an intermediate low viscosity fluid stage to permit said resin to be dispersed, as by capillary action, between each of the laminations of core assembly whereby to serve as a bonding agent therefor in its cured or set state binding all of the laminations in said core assembly into a rigid body, said resin, in its cured state being characterized by high thermal stability.

Still another object of this invention is the provision of a core construction as described above wherein the laminations thereof may be bonded one to the other in a rigid mass to result in a substantial decrease in the noiseforming characteristics of the said core, said bonding agent comprising a polymerizable epoxy resin system which may be temperature or catalytically cured or set and said uncured composition being applied by dipping or brushing onto the edges of said laminations when same are assembled and clamped to form a core construction assembly, said resin being chosen so that a low viscosity intermediate product is formed during the curing or setting thereof thereby introducing, as by capillary action, said bonding agent between the individual laminations, and completing the curing or setting of said resin system to form a substantially permanently bonded unit which remains rigid during subsequent conditions of manufacture and operation.

Still a further object of the invention is the provision of a novel clamping member which is formed of an extremely economical material, such as pressed fiberboard or paperboard used for maintaining the ends of the core in assembly while the cementitious material is setting.

A further object of the invention is the provision of an electromagnetic device formed with a laminated core in which, during the course of manufacture, :a clamp is used to maintain the core in assembly but which clamp readily may be removed and discarded after the core has become a bonded integral structure.

Other objects of the invention will occur to those skilled in this art as a description of the invention herein proceeds, in connection with which the drawings illustrate preferred methods of making the electromagnetic device and the structures resulting therefrom.

In the drawings:

FIG. 1 is a perspective view of an electromagnetic apparatus consisting of a transformer for use in a fluorescent lamp circuit which has been constructed in accordance with the invention, but the same being illustrated with one of the clamps of the invention disposed in exploded relation to an end of the core.

FIG. 2 is a perspective view showing a method of applying the thermo-setting resinous material to the parts of the transformer core shown in FIG. 1.

FIG. 3 is an exaggerated sectional view showing the manner in which the cementitious material penetrates into the core while it is curing.

FIG. 4 is a perspective view showing another method of applying the cementitious material to the core.

The invention is based in part upon a discovery that certain polymerizable resins having epoxy polyurethane or equivalent based constituents which are available on the market have unusual bonding powers of sufficient degree to retain steel laminations in assembly. In the shell type of core which utilizes a plurality of core members which must be held together, such resins applied to the abutting lamination end faces and clamped in this association were found not only to result in a bonding together of the clamped members but as well to penetrate between the laminations and cause the individual laminations to be adhered face to face in a compact unitary structure. In order to enable the clamping together of the ends of the core forming the electromagnetic devices, the invention contemplates the use of a simple rectangular ring of paperboard or fiberboard readily crushable to enable the variations in the lamination dimensions to be accommodated, but yet having sufiicient strength to retain the core in assembly while the resin is curing. Such rings or clamps are extremely economical and obviously can be permitted to remain in place upon the ballast or stripped from the ballast and discarded. In accordance with the invention the ballast laminations are suitably adapted, as by notching, to retain such disposable binders and to thereby be retained in assembled relation during the noted curing. Such rings are also highly economical and simple to manufacture by merely stamping the same from sheets of paperboard or fiberboard. In the ensuing description a preferred resin or cement of the epoxy or urethane type will be utilized; however, this is not meant to be a limitation of the scope of the invention to such type resin. Even polyester based resins having tensile strength properties so as to solidly adhere the laminations one to the other may suffice.

Referring now particularly to the drawings, FIG. 1 illustrates a transformer which is made up of three parts, a pair of elongate outer F-shaped legs 12 and 14, and a center T-shaped leg 16. Each of these three parts is formed of a stack of laminations, the laminations of each respective part being identical in configuration. Obviously it is intended that each of the stacks be of the same height.

As viewed in FIG. 1, the parts 12 and 14 are arranged with their right angle legs 18 and 20 at the upper end of the view, and the intermediate extensions 22 and 24 forming shunts in a manner well known. The center T-shaped leg 16 has its cross-head 19 at the bottom of the view abutted between the lower ends of the respective side parts 12 and 14 while the major portion thereof comprising the central winding leg 30 of the core passes through a pair of windings 26 and 28 disposed on the said central winding leg in windows which are formed in a manner well known. Suitable terminal boards 32 and 34 are held to the windings by means of adhesive tape or the like and the various connections from the windings 26 and 28 are brought out and soldered to the terminals of the terminal boards.

The lower ends of the side members 12 and 14 are identified by the reference numerals 36 and 38 while the upper end of the central winding leg 30 is identified by the reference numerals 40. It will be seen that in the assembly of the ballast, the legs 18, 20 and end 40 are disposed in face-on abutting relationship along two joints 42 and 44 while a similar arrangement is provided at the bottom end of the core due to the abutting relationship of the ends 36, 19 and 38. That is, the upper side member ends 18, 4t and the lower ends 36, 38 are respectively bridged by center leg ends 40, 19,

For the purposes of describing this view, it may be assumed that the joints 42 and 44 and the equivalent joints at the bottom of the core have been provided by bonded and cured epoxy or urethane resin, and that the resulting core structure of the transformer 10 is a unitary assemblage, rigid and immovable, not only with respect to the parts 12, 14 and 16 but as well with respect to the individual laminations making up the parts. In the course of building the ballast, or electromagnetic device, first the central winding leg 38 will have the two windings 26 and 28 assembled thereto by passing the said central winding leg through the centers of the windings into the tubular paper forms upon which the windings are formed. These two windings are adjusted along the length of the central winding leg with one winding such as winding 28 usually abutting against the cross-head 19 of the T and the other winding 26 spaced sufiiciently from winding 28 to be accommodated in the windows which will be formed when the parts of the electromagnetic device are assembled. Thereafter the stacks of laminations forming the side parts 12 and 14 are assembled to the central winding leg over the windings 26 and 28 having previously been treated with the cementitious material, such as the epoxy or urethane resin or cement referred to, and the ends are clamped together.

In order to clamp the ends of the electromagnetic device together during the setting of the epoxy or urethane resin or cement, notches such as shown at 50 are provided at the four corners of the core structure. These notches are no different from those heretofore used in electromagnetic devices which utilized metal clamps. In this case, however, instead of metal clamps, rectangular rings 52 are engaged over each end of the electromagnetic device. Each ring has a central recess 54 which fits the assembled core ends, the recess being formed at the same time that the rings are stamped. The recess may be formed slightly smaller in its interior dimensions than the maximum dimensions of the ends of the core. The material from which the rings preferably are made is paperboard or fiberboard of some kind which is crushable so that the ring may be forced on to the ends of the core and will tightly hold the portions of the core as well as the laminations in assembled condition without any danger of movement.

It will be appreciated that the strength of the ring need not be sufficient to enable dependence upon such ring for maintaining the ends of the core in assembled condition permanently without other means being used. The only function required of the rings in this usage thereof is to maintain assembly until the cement has set or cured, and for this purpose the rings are more than suificient. The exploded portion of FIG. 1 illustrates the manner in which the ring is installed or removed. An arbor press or ram may be used. The rings may be left in place after the core has been formed, and the cement set or cured, or the rings may be removed if it is desired to keep the size of the core as small as possible and eliminate possible pressure points against lead wires, it is immaterial which. Often the adhesive may run onto the ring and thereby prevent its ready removal in which case it may be left in position.

In applying the epoxy 0r urethane resin or cement to the portions of the electromagnetic device 10, several different methods may be used. In FIG. 2, the central T-shaped member 16 and the side members 12 and 14 are shown being painted with the adhesive or cementitious material which is designated 56, on the contemplated abutting surfaces, by means of the brushes 58. There will be two opposite surfaces or end faces of the end of the member 16 and the inside surface of each of the side members 12 and 14 respectively. Obviously similar surfaces at the lower end of the core will be. painted with the cement.

in FIG. 4, another method is shown in which the entire end of the core member is dipped into a container of the urethane or epoxy resin or cement such as shown at 60. When this is done, the windings 26 and 28 or any other windings which are intended to be mounted on the central winding leg are already in position. Obviouslythe stacks must be held together by some suitable means during this process although it is a simple matter for the Workman who is assembling the device to hold the stacks of the side members 12 and 14, for example, in hishand While this is being done and slip the rings 52 over the ends after the core has been assembled.

One property of the reins suitable have, such as urethane of epoxy resins has been found to be of great advantage. Although epoxy resins will be referred to hereafter, by way of example, to explain certain features of the invention, other resins such as the urethanes are not precluded. The epoxy cements as they are used today are of rather viscous consistency and do not run rapidly or readily into the interstices between the laminations. Just before the set or cure, however, the physical properties of the, epoxy cement, for instance undergo a change which renders them very fluid and penetrating. At this point it has been found that the epoxy cement will penetrate into the interstices between the laminations somewhat asshown in the exaggerated view of FIG. 3, and by capillary action the epoxy cement will. be drawn to a great extent transversely almost to the very outer ends of, the laminations, thereby providing a very strong bond, not only between the two portions which are, abutted but as well between the face toface surfaces of theindividual laminations. In FIG. 3, for example, thereis illustrated in section the abutting juncture or joint 42 between the side parts 12 and the central part 16. The epoxy resin or cement 56- provides a bond between the abutting faces of the parts 12 and 16, and the epoxy resin or cement 56' which has run between the surfaces of the individual laminations provides the advantageous assembly of the entire apparatus into an integral structure. The epoxy cement is shown in the view in its cured condition by means of the dark areas between laminations.

It is feasible to use some manner of flexible or extensible member other than the paperboard or fiberboard ring 52 to hold the ends of the core in assembled condition while the epoxy resin or cement is curing. It is preferable that such a member have the property of being able to apply fairly even pressure upon each and every lamination of the assemblage, so that when the cure occurs, there will be no misplaced laminations or air spaces. It is believed that there has been no successful bonding of the ends of electromagnetic devices comprising laminated cores with such thermo-setting resins.

It is also desired to point out that other cementitious or bonding materials may be used advantageously with the rings 52 and that after such cementitious materials have set, the entire assemblage may be impregnated with varnish and baked and/or encapsulated in some plastic or potting compound, thereby adding overall rigidity to the assemblage and relieving some of the strain from the rings 52. Under such conditions, of course, it is intended that the rings will remain in position on the completed electromagnetic device.

The retaining rings 52 instead of being made of paperboard and fiberboard may in certain instances he of a semi-permanent nature, being made of synthetic resins, such as nylon or other plastics, which while to some extent yieldable nevertheless have great strength. The yieldability, on the interior of the ring at least, is to accommodate variations in stock size and lamination dimensions. Whether of paperboard, fiberboard or plastic, the ring should be able to withstand the temperatures 6, to which the electromagnetic device may be subjected before the adhesive has set or is cured.

In using the method of the invention, the curing of the cementitious or resinous material may take place in several ways. It may be-permitted to take place in air; it may be accelerated by baking in an oven; it may occur as a result of potting withno potting compound; it may occur simultaneously with another procedure such as varnishing and/or baking the varnish.

Although many resins are suitable for use with the invention, it is preferred to utilize those of the group epichlorohydrin bisphenol-A which has been catalyzed by an acid anhydride. To speed the curing or setting of the resin system, a small amount of an accelerator may be added, such as for example, a tertiary amine, or commercially available dimethylamino methyl-phenol, tridimethyl amino methyl phenol, and the like.

An exemplary formulation was successfully utilized to prepare a core of the character described. Such for.- mulation as described below is to be considered solely for the purpose of illustrating the practice of the invention andin no manner is to be considered as a limitation to the scope of the invention as described in the claims appended hereto.

The successful formulation was asfollows:

10 parts epoxy resin of the bisphenol A-epichlorohydrin type 6 parts hexahydrophthalic anhydride.

.1 part tridimethyl amino methyl phenol (DMP 30) The core laminations were assembled into stacks to form the core parts and subsequently assembled to form the core construction. The clamp rings were placed on opposite ends of the core assembly and the composition was brushed. on the edges thereof. The core assembly with the brushedaon coating was exposed to. centigrade for 50 minutes in an oven. When the core assembly was removed from the oven, the resinous composition was found to be cured and had become a rigid mass. The clamping rings were then removed and the assembly was held intact by the polymerized resinous composition. On subsequent testing and operation the finished transformer core was found to be operative with less production of noise. The core was subsequently taken apart and the residual evidence showed that the resin had entered the interstices between laminations and had firmly bonded same together.

Obviously variations in the methods and structures can be made without departing from the spirit or scope of the invention.

What it is desired to secure by Letters Patent of the United States is:

1. A core construction formed of laminations which include a stacked assembly of individual lamination parts, at least one of said parts having bridged ends forming the outer framework of said core and another of said parts forming the central winding leg of said core adapted to be disposed within said outer framework and between the bridged ends thereof, means comprising a pair of removable clamp members disposed on opposite ends of said core parts to hold same in assembled condition, bonding means for permanently retaining said laminations in position with the occurrence of a minimum displacement of individual laminations throughout further utilization of said core construction, said bonding means comprising an outer coating of a polymerized epoxy resinous composition disposed on outer end faces of said laminations and a portion of said coating which has penetrated between the laminations during the setting of said composition, said epoxy resinous composition being characterized by a low viscosity transient fluid state during the setting thereof.

2. The core construction as claimed in claim 1 in which said removable clamp members are formed of paper and have a dimension only slightly less than the perimeter of the ends of said core whereby the said clamp members may be tightly secured around said ends.

3. The core construction as claimed in claim 1 in which said removable clamp members are formed of organic material and have dimensions chosen so that said members are tightly engaged with the ends of said core, and said members are adapted to be removed from said core ends after the setting of said resinous composition.

4. A core construction formed of laminations which include the rectangular outer framework formation having a window therein and a central elongate formation disposed within said framework to form .a central winding leg, the invention comprising a notched portion in said laminations adapted for receiving a low strength, disposable binder for holding said laminations in assembled relation, a polymerizable binding agent disposed on end faces of said laminations and between adjacent laminations, said binding agent characterized by a low viscosity fluid state during a first stage in the binding thereof, whereby said disposable binder is effective for holding said laminations in adjacent relation during the low viscosity state of said binding agent, and said bonding agent being polymerizable to a second substantially permanently rigid, distortionfree state for bonding end faces of said adjacent laminations.

5. A transformer core construction comprising an assembly of individual electrical steel lamination parts arranged in stacks to form the operative parts of said core construction, said parts being bonded together by cementitious material therebetween, and removable clamp means comprising a pair of ring members adapted to be disposed on the ends of said assembly for maintaining the same in assembled condition, said ring members adapted to be tightly secured onto said ends of said assembly, in which said ring members are made of paper material.

6. A core construction formed of laminations which include a rectangular outer framework formation having a window therein and a central elongate formation disposed within said framework to form a central winding leg, the invention comprising, a polymerizable bonding agent disposed on end faces of said laminations and, adjacently to said lamination faces, the plane juxtaposed surfaces of said laminations, said bonding agent characterized by a low viscosity fluid stage during a first stage in the polymerization thereof, said laminations having substantially planar surfaces juxtaposed for abetting capillary flow of bonding agent therebetween from said end faces in a low viscosity state of said bonding agent, and said laminations being adapted and configured for having said substantially planar surfaces retained in juxtaposed relation by a low strength disposable binder in a low viscosity state of said bonding agent and said bonding agent being polymerizable to a second, substantially permanently rigid, distortion-free state of bonding juxtaposed surfaces and end faces of said adjacent laminations.

References Cited by the Examiner UNITED STATES PATENTS 2,280,981 4/1942 Schuh 336-219 2,293,951 8/1942 Seastone et al 336-234 X 2,429,604 10/1947 Boucher et al 336-210 X 2,563,105 8/1951 Epstein 336-210 X 2,579,560 12/1951 Ford 336-219 X 2,671,951 3/ 1954- Sliwiak 29-15561 2,822,483 2/1958 De Jean et a1. 310- 2,838,703 6/1958 Balke 310-217 2,947,909 8/1960 Berger 336- 2,958,931 11/1960 Hurt 29-15561 3,029,403 4/1962 Krueger 336-219 3,122,667 2/1964 Baciu 310-45 JOHN F. BURNS, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,222,626 December 7, 1965 Albert E. Feinberg et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 14, for "reins" read resins column 7, lines l6, l8, l9 and 22, for binding", each occurrence, re bonding Signed and sealed this 11th day of October 1966.

(SEAIJ Anna;

EKNUARD l BRENNER Commissioner of Patents 

5. A TRANSFORMER CORE CONSTRUCTION COMPRISING AN ASSEMBLY OF INDIVIDUAL ELECTRICAL STEEL LAMINATION PARTS ARRANGED IN STACKS TO FORM THE OPERATIVE PARTS OF SAID CORE CONSTRUCTION, SAID PARTS BEING BONDED TOGETHER BY CEMENTITIOUS MATERIAL THEREBETWEEN, AND REMOVABLE CLAMP MEANS COMPRISING A PAIR OF RING MEMBERS ADAPTED TO BE DISPOSED ON THE ENDS OF SAID ASSEMBLY FOR MAINTAINING THE SAME IN ASSEMBLED CONDITION, SAID RING MEMBERS ADAPTED TO BE TIGHTLY SECURED ONTO SAID ENDS OF SAID ASSEMBLY, IN WHICH SAID RING MEMBERS ARE MADE OF PAPER MATERIAL. 